Many electrical devices such as motors and transformers generate heat during operation. In some instances, due to overload, short-circuiting or other malfunctions, the devices may overheat to the point of destruction. In order to minimize damage when such overheating occurs, most electrical devices include thermal protection sensors which are usually wired into the operating circuit. These sensors monitor the operation of the device and interrupt the circuit if excessive temperatures are reached.
A typical use for such thermal protection sensors is in an electrical transformer, such as a ballast transformer in a fluorescent lighting fixture, to sense overheating and interrupt the power supply. Such transformers are usually disposed in a housing and insulated to protect the transformer by encasing in pitch. In order for a thermal protection sensor to work properly, it should be positioned in contact with a coil of the transformer and maintain that contact during the life of the device. Plastic clips are often used to hold the thermal protection sensor in the transformer housing, with the clip taped, glued or otherwise attached to the housing to prevent movement. An example of a typical prior art clip is shown in FIG. 1.
It has been found that the prior art clips do not provide uniformity in sensing as they rely on proximity rather than full contact with the electrical device. The sensor will vary in distance from the device, due to slight variations in the transformer coil configuration, sensor shape or housing dimensions. In addition, movement of the clip, either during transformer insulation or handling of the transformer, may similarly result in inconsistent sensing between devices. Therefore, it is desired to provide a clip which assures uniformity of contact, providing means for accurately positioning and maintaining contact during the life of the electrical device, thereby assuring optimum thermal protection.